


Steel-Strike Moonsault

by RyuuseiRiderJackie



Series: Rider!Izuku One Shots [5]
Category: Kamen Rider Build, 僕のヒーローアカデミア | Boku no Hero Academia | My Hero Academia
Genre: All For One and One For All Do Not Exist, Alternate Universe - Canon Divergence, But That Doesn't Mean Powerless!, Crossovers & Fandom Fusions, F/M, Midoriya Izuku Has Amnesia, Quirkless Midoriya Izuku, U.A. is a University (My Hero Academia), mentioned Human Experimentation, tell me if I should add tags
Language: English
Status: Completed
Published: 2021-01-02
Updated: 2021-01-02
Packaged: 2021-03-10 23:15:36
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,214
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28495197
Author URL: https://archiveofourown.org/users/RyuuseiRiderJackie/pseuds/RyuuseiRiderJackie
Summary: The day of the USJ attack, Kyoka and Izuku become desperate for answers of the past.(Kamen Rider Build!Izuku One-shot)
Relationships: Jirou Kyouka/Midoriya Izuku, implied
Series: Rider!Izuku One Shots [5]
Series URL: https://archiveofourown.org/series/2001289
Comments: 1
Kudos: 8





	Steel-Strike Moonsault

**Author's Note:**

> I've been wanting to do this for at least a week or so now.

“Stay back! This is real…. Those are villains!” Aizawa shouts to his class, his hands clenching around his capture weapon. “Thirteen, get them out of here! I’ll take care of the fodder.”

“Eraserhead!” The voice of his student, Izuku Midoirya, shouts, Aizawa turning to meet eyes with the young adult. Izuku stands at near the same height as him, with messy green hair that meets at pitch black roots. His eyes are cracked like shattered glass, with the fragments formed into a bright blue in his right eye, and a burning red in his left. He wears his rather casual looking hero outfit, composed of a tan trench coat, a white long sleeve hoodie adorned with red and blue stripes, torn jeans, and a pair of mismatched high tops of red and blue. “There’s no way you can take on those villains by yourself. Not all of them at least. Sure you’ll be able to get a good number of them, but the calculations… It’s not logical.”

Aizawa keeps his steely expression, but underneath it all he knows the young adult is right. He’s up against at least a hundred or so villains in the center of the complex alone, no telling if this is all there is or not. But, the students, though in college they may be, are still too young and inexperienced to be taking care of something like this. “Even so… I must protect you all while I can. Go, get to safety. I’m counting on you, Midoriya.” Aizawa turns and jumps down the stairs, leaving the class behind.

Izuku grimaces, before turning around and facing his class. “Ah mou… This is the worst…” He says to himself, running alongside them as they move towards the exit.

“ **Sorry, kiddo’s, but I can’t quite let you leave.** ” A playfully malicious voice echoes around the students, as grey mist surrounds them, before swirling around into a single point, as a figure appears from within. Dressed in blood red armor, translucent teal marks the eyes and chest of the figure, as they step out. “ **See, we at Faust were told that there were quite a few quirks worth looking into here, and in pursuit of Pandora’s Quirk… Well, how could we refuse? Now then…** ” The armored figure points at the form of one Ochako Uraraka, a chuckle leaving his lungs. “ **Zero Gravity girl, would you mind coming with me?** ”

Ochako takes a step back in fear, as the villain chuckles further. In a few steps, she bumps into a figure behind her, causing her to pause in fear as she turns to face the person. Behind her looms a large figure, skin adorned in black, with equally dark metal fused into it, with bulbous protrusions shooting up from its shoulders. It lets out a pained wheeze as it tries to grab at Ochako.

“Oh no you don’t!” Izuku and another classmate shout, one Kyoka Jirou, as they rush at the creature. Izuku pulls out a small red bottle, with the face of a Rabbit on it, as Kyoka pulls out a similar purple bottle with a Dragon’s face. The two shake their respective bottles, a purple flame-like energy surrounding Kyoka, as red streams of wind circle around Izuku’s limbs like springs. The two punch at the creature, sending it staggering back.

The red armored figure tilts his head in intrigue, before letting out a soft chuckle. “ **Well, who would have expected to see previous experiments in this little game?!** ” He announces, spinning in place with some sort of sick glee. The two look at the man in shock, before the shock quickly turns to anger on Kyoka’s end. “ **Oh but it makes sense I suppose. A sort of want to never have anyone go through what you did. Of course…** ” The man raises some sort of modern-yet-steampunk rifle with a sort of sadistic glee, “ **Do not think I’ll let you two ruin the fun so easily.** ” The man fires the weapon, causing mist to surround the students rapidly.

Kyoka grabs onto Izuku’s arm as the mist envelops them fully. The two go from standing to falling in a matter of seconds, before they find themselves against rocky ground, with another of their classmate’s, Momo Yaoyorozu, nearby. The two pick themselves up quickly looking at their surroundings. “We need to get to the center/stairs.” They say at the same time, both quickly looking at each other in surprise.

“Aizawa isn’t going to be able to hold off all of those villains, he needs help.” Izuku says, pulling out a hunk of black metal, with minor red and silver paint applications. He slaps it against his waist, a bright yellow belt wrapping around his body. “We need to assist.”

“That man said experiments! We need to get after him and beat the info of what they did to you out of him!” Kyoka shouts, her bottle beginning to glow brighter, as a small, blocky, mechanical dragon, painted in a deep purple flies to their location. “I get helping Aizawa, but I’m sure taking out that asshole would be some pretty good help too! He might even know why we suddenly got super strength too!”

“Jirou, we can’t just abandon our teacher!” Izuku shouts back, taking a blue bottle adorned with a tank out from his pocket.

“I’m not saying we abandon him! Hell, you can stay in the center and help him if you want, but I want answers, damnit!” Kyoka shouts back, the jacks on her ears flailing in anger.

“The both of you calm down!” Momo shouts, throwing a metal pole between them, as it hits some kind of humanoid robot. “We have more pressing matters to worry about!” She shouts, as she produces another pair of metal poles, now identifiable as bo staffs.

Izuku and Kyoka simply look at each other and sigh, before turning their attention to the minions surrounding them. “We can argue later.” Izuku says, getting a nod from Kyoka. Izuku proceeds to shake both of the bottles, before twisting open the caps on the top. He places the bottles into his belt, small overlays appearing as he does so.

**“RABBIT! TANK! BEST MATCH!”** The belt announces, lights pouring from a circular port on the side. Izuku begins to spin the crank on the side, pipes of red and blue liquid forming from out of the belt, twisting into a humanoid shape. Izuku finishes cranking the handle, as he holds a fist next to his face, an open palm sent forward.  **“ARE YOU READY?!”**

“Henshin!” He shouts as he crosses his arms in an ‘X’ for a moment, before slamming his arms to his sides.

The pipes slam down on top of him, covering him in the liquid, now turning to metal in a moment, steam pouring off from the sudden impact.  **“THE STEEL-STRIKING MOONSAULT! RABBITTANK! YEAH!!”** The belt announces, as the armor completes.

Red and blue mixed in a diagonal pattern, with eyes shaped like a rabbit head and tank, a rabbit’s paw and tank tread each covering a foot respectively. “I suppose for now, we’ll just have to take care of this.” Izuku says, raising his fists before charging forwards.

“Ugh, whatever. But we’re not done talking about this!” Kyoka shouts, shaking her own bottle more, as she rushes forwards, punching at the robots with the same purple energy as before, the small purple dragon spitting out neon purple flames alongside of her.

* * *

Aizawa ducks and weaves beneath the hazmat suit covered villains, deactivating quirks left and right. He wraps his capture scarf around one of their wrists, flipping the villain over his shoulder. He blocks a rock covered fist, chopping at this villain’s neck, before throwing them into another villain.

“ **Hmm, your time limit is whittling down more and more.** ” The grainy voice of another man in armor speaks. Black armor with green and red tubing, leading into a yellow bat chestplate, with yellow eyes on the helmet. “ **With each moment you erase one of their quirks, you get closer and closer to a time limit of twenty seconds. I imagine if I let you keep at it with your quirk, you’ll eventually get to twelve seconds, eleven, maybe even more. Of course, you must realize the meaning behind my words.** ” The bat armored man pulls out a modern-steampunk pistol, almost looking like an incomplete version of the rifle the cobra man had used earlier. He takes aim at Aizawa before firing out a series of attacks, each hitting the man in the arm.

Aizawa grabs a villain and uses them as a meat shield, running up closer to the bat man. “ **Oh? Surprising to see a hero use such a dirty tactic. Of course, you’re not exactly a spotlight, so I guess it makes sense.** ” Aizawa tosses his hostage villain aside, grabbing at his capture weapon with his undamaged hand, only for the weapon to be caught by the monster from the stairway instead. Aizawa looks at the creature in shock, before suddenly being pulled towards it, a monstrous fist slamming into his face. “ **I saw that look of shock in your eyes, you’ve never encountered one of these before, have you?** ” The bat taunts, walking over to the still stunned Aizawa, pulling out a modern-steampunk sword, the missing half of the rifle, as he does so. The monster grabs a hold of the stunned hero, slamming his face into the concrete. “ **This creature is called a Smash. More specifically, this is a Clone Smash, created from battle data of the original, who was unfortunately defeated in the testing phase. It’s not as intelligent as the original, but…** ” Aizawa is shoved further into the concrete. “ **It’s just as violent.** **Of course, this information won’t serve you well at all, since you’re about to become a sacrifice for the great cause, of creating Pandora’s Quirk.** ” The man lifts the sword, twisting it in hand to stab downwards into Aizawa’s back.

**“THE LONG-CALL LONE-WOLF! SMARTPHOWOLF! YEAH!”** A familiar voice echoes out, as a tri-set of silver claws slashes against the bat man’s armor, sending him flying back. A large, sharp, rectangular shield in the appearance of a giant smartphone slams into the Clone Smash, sending it staggering away, freeing Aizawa, and giving him a chance to look up at his savior.

Izuku, in a blue and silver set of armor, with a blue phone app for one eye and a silver wolf for the other, looks at his professor, reaching down a blue metal clad hand to help the man up. “I thought I told you to run away.” Aizawa speaks, getting up to his feet with assistance.

“That was the original plan, but the cobra equivalent of that guy showed up and warped a bunch of us to different locations.” Kyoka runs up, wrapping the man’s arm around her shoulders, Momo running up and doing the same with his injured limb.

Izuku finally takes notice of the man, taking a step towards him, as the bat man slowly recovers. “It’s you… The man from my memories…” He says, Kyoka looking at him.

“Wait… That’s the bat man?! I thought you meant he had a bat quirk, not…” Kyoka speaks, before glaring at the villain. “What’s the big idea, asshole?! Kidnapping people, teens and adults alike, forcing them into weird green pools, and making ‘em inhale a bunch of gas?!”

The bat man merely shakes his head, as red mist begins to form next him, the cobra man appearing from within it. “ **Sorry to cut your test short, but the engine leg boy got out. It’s likely he’s on his way to get help right now.** ” He says, before looking at the small audience. “ **Oh, hello again, my dear experiments! Oh, and I see you finished that childhood dream of yours, Green Boyo! Good to see that!** ”

Izuku’s breathing stops, and Kyoka can hear his heart rate rocket. She looks at the boy in shock, as his entire body begins to rattle. “ **You…** ” Izuku speaks, his voice dripping with venom. “ **You bastard!!!** ” He yells, rushing forwards. The bat man steps to the side, as Izuku tackles the cobra man to the ground, hitting him with his fists over and over. “Why did you kidnap me?! Why did you experiment on me?! Give me back my body! GIVE ME BACK MY MEMORIES!!!” Izuku yells, grabbing the man by the collar of his armor.

“ **Three point three, point four, point five! Incredible! Who would have ever guessed that rage would be able to increase a Hazard Level like this!** ” The cobra man laughs, before punching Izuku in the chest, sending the boy flying back, falling onto the arena floor, his armor dissipating. “ **Ah, but sorry kiddo! I can’t do much with giving you those answers, quite yet! I’ve got a pretty good game planned after all. Oi, Rogue, I’d say it’s about time we head out, if we don’t want to have to deal with anymore pesky heroes.** ”

The bat man, Rogue, begins to walk back over, giving one last glance at the students and teacher. “ **We will meet again. Stalk, leave them a parting gift.** ” Rogue speaks, walking into a cloud of grey mist. The cobra man, Stalk, gives a chuckle, before twisting a small gear on the side of his rifle. 

**“DEVIL STEAM!”** The weapon announces, before Stalk takes aim. He fires it off, the bullet seeming to change trajectory in midair, as it curves away from the still downed Izuku, and hits the Smash in the chest. The monster convulses with energy, swelling a bit in size, as it lets out an ear ringing screech.

“ **I’d say you have about ten minutes before it destroys everything in here. Have fun with that, Green, Purple. Ciao!** ” Stalk turns away, disappearing into a cloud of red mist.

The Smash lets out another screech, before it takes a step forwards, creating a small crater just on impact alone.

“Izuku, you need to transform now!” Kyoka shouts, looking at her still downed friend. “Izuku? Izuku, come on, now's not the time to be making me worry like this. Seriously, get up man!”

“He called me Green Boyo!” Izuku shouts, causing Kyoka to flinch. “The only one who called me that name… Was the guy who took me in the first place!” Izuku slams a fist into the ground. “You were right, I should have gone after him, while you stayed here! Maybe… Maybe then I-”

“You what? Could have gotten hurt without me there? Izuku, you weren’t wrong, I was. I’m so focused on trying to figure out why all this shit happened to us, that I keep forgetting our promise. We’re going to be heroes for Love and Peace right? Then show us what that means, and kick this Smash’s ass!” Kyoka shouts, Izuku pushing himself up off of the ground, as he gives a shaky nod.

“Right… Who I was doesn’t matter. I’m Izuku Midoriya, the one who will become Build!” Izuku shouts, pulling out an orange and grey bottle. “Now, shall we begin the experiment?” He asks, before he begins to shake the bottles, complicated looking physics equations seeming to form beside him, before he twists open the caps, and places the bottles into his belt.

**“HAWK! GATLING! BEST MATCH!”** Izuku cranks the handle, orange and grey liquid forming this time.  **“ARE YOU READY?”**

“Henshin!”

**“THE SOARING RAMPAGER! HAWKGATLING! YEAH!”** Orange and Grey slam on top of Izuku, as a giant pair of orange wings form on his back, spreading out for a few moments, before shrinking down. Izuku lifts his head, raising his arm also as he does so.

“HawkGatlinger!” He shouts, tubing forming into a large pistol sized orange and grey gatling gun in the palm of his hand. He grabs a solid hold of it, before turning focus back to the Smash. He puts up his pointer finger, sliding it against the wing of his Hawk eye, the light catching in his gatling barrel eye. “I’ve got… The law of victory down!” He announces, before jumping up, his wings granting him flight, as he begins to fire upon the monster.

Kyoka shifts Aizawa’s arm on her shoulder with a smirk, before she and Momo start moving towards the stairs. “Jirou…” Aizawa starts, the violette looking at him with curiosity. “When this is all over, I fully expect an explanation as to why you and Midoriya recognized those guys, and what they have to do with Midoriya’s disappearance at the age of twelve, leading up to his retrieval and subsequent discovery of memory loss at age seventeen.”

“Well, it’s complicated… But, yes sir.” Kyoka replies, as the trio continue moving.

Back with Izuku, the boy dodges the large slow swing of the enlarged Smash’s fist, before firing more attacks from his gun. “This thing seriously needs to go down!” He shouts to himself, gripping the gun in his left hand, as he begins to crank the handle of his belt with his right. He slides the middle of the gun down his side multiple times, as he begins to fly higher up inside of the domes arena.

**“TEN! TWENTY! THIRTY! FOURTY! FIFTY! SIXTY! SEVENTY! EIGHTY! NINETY! ONE HUNDRED! FULL BULLETS!! / READY, GO!!”** The gun and belt announce at the same time, as white grid lines thrust the smash into the sky, before forming into the curved circumferences of a sphere.

Izuku flies throughout the sphere, firing orange holographic hawks from his gun, hitting the monster with each one. Finally, at the hundredth hawk, Izuku joins alongside it, soaring towards the Smash, before drop kicking through the monster, causing it to explode in a mass of green flames.

Izuku lands on the ground with a solid thud, before he takes the bottles out from his belt, his armor dissipating soon after. Soon a resounding crash echoes through the dome, as the doors come flying off their hinges. All Might was now here…

And the battle was already over.

* * *

Izuku sat on the edge of an ambulance, shock blanket wrapped around him, as he stares at the Rabbit bottle. A sudden shifting of weight alerts him to a presence next to him, causing him to turn his head, seeing Kyoka sitting next to him, with her own Dragon bottle in hand. “Sorry, again.” She says, Izuku letting out a sigh.

“I think both of us will be apologizing until the end of time at this rate, so let’s just… Let’s leave well enough alone.” Izuku says, Kyoka giving a small, if hesitant nod in response. “Besides, like Rogue said, they’ll see us soon. We’ll just get answers then.”

“Izuku…”

Izuku smiles. “We both lost sight of our goal today, but not again. We’ll be heroes who bring smiles to all who see us, and with these hands… We’ll build a future of Love and Peace.” Izuku clutches his bottle in a fist, before raising it up camly next to Kyoka. “Right?”

Kyoka smirks, tapping her own bottle holding fist against Izuku’s. “Right.” She says, before shuffling in closer next to Izuku. “For now though, I just want to relax.”

  
  


“That… That sounds nice.” Izuku says, allowing himself to relax into Kyoka as well, the two sitting comfortably next each other.

  
  
  
  
  


A Best Match waiting to happen.

**Author's Note:**

> FIGURING OUT HOW TO DO BUILD IZUKU FELT SO GOOD.
> 
> Also, this could be considered another testing the water fic. Seeing if there's interest in this concept, and if there is, I might make this a full series as well, like Geed!Izuku.
> 
> Speaking of, I've decided to make Flipping Genetic Destiny a low priority fic, meaning while that it's going to have less update compared to other stories. With that in mind, thanks for reading, and have a nice time!


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